
154 Optical Fiber Communication Systems with MATLAB
®
and Simulink
®
Models
response
the
rise-time
constant
has
to
be
minimized.
Some
common
types
of
semicon-
ductor
lasers,
commercially
available
in
the
production,
are
FP
lasers,
DFB
lasers,
distrib-
uted
Bragg
reector
(DBR)
lasers,
single
quantum
well
(SQW)
lasers,
multi-quantum
well
(MQW)
lasers,
constricted-mesa
lasers,
and
buried
heterostructure
(BH)
lasers.
In
addi-
tion,
currently
coherent
transmission
systems
require
narrow
linewidth
light
wave
source
with
a
3
dB
bandwidth
of
around
100
kHz
or
even
less,
the
external
cavity
is
then
to
be
inserted
to
reect
only
the
single-frequency
lasi